An abnormal skin area calculating system and a calculating method thereof are provided. The system includes an image capture module, a database, a skin analysis module, and a numerical calculation module. The database pre-stores at least one abnormal skin analysis data. The skin analysis module analyzes and marks an abnormal skin area in a skin image by using the skin analysis data. The numerical calculation module calculates a pixel area of the abnormal skin area graph, and calculates an actual skin area of a human body corresponding to the abnormal skin area graph with an area calibration parameter. The area calibration parameter is pre-stored in the database, or is generated by the numerical calculation module in calculating a transformation relation between a presented calibration length unit and a pixel distance unit according to a calibration object graph in the skin image.
